﻿using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

namespace FuiouCode {
    public class RSAFromPkc8 {

        /// <summary>
        /// 签名
        /// </summary>
        /// <param name="content">待签名字符串</param>
        /// <param name="privateKey">私钥</param>
        /// <param name="input_charset">编码格式</param>
        /// <returns>签名后字符串</returns>
        public static string sign(string content, string privateKey, string input_charset) {
            Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);

            byte[] Data = Encoding.GetEncoding(input_charset).GetBytes(content);

            RSACryptoServiceProvider rsa = DecodePemPrivateKey(privateKey);

            MD5 sh = new MD5CryptoServiceProvider();//这里也可以使用MD5加密方式
            //SHA1 sh = new SHA1CryptoServiceProvider();
            byte[] signData = rsa.SignData(Data, sh);
            string str = Convert.ToBase64String(signData);
            //str = str.Replace("+", "%2B");
            return str;
        }

        /// <summary>
        /// 验签
        /// </summary>
        /// <param name="content">待验签字符串</param>
        /// <param name="signedString">签名</param>
        /// <param name="publicKey">公钥</param>
        /// <param name="input_charset">编码格式</param>
        /// <returns>true(通过)，false(不通过)</returns>
        public static bool verify(string content, string signedString, string publicKey, string input_charset) {
            Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);

            byte[] Data = Encoding.GetEncoding(input_charset).GetBytes(content);
            byte[] data = Convert.FromBase64String(signedString);
            RSAParameters paraPub = ConvertFromPublicKey(publicKey);
            RSACryptoServiceProvider rsaPub = new RSACryptoServiceProvider();
            rsaPub.ImportParameters(paraPub);
            MD5 sh = new MD5CryptoServiceProvider();//这里可以使用MD5加密方式
                                                    //SHA1 sh = new SHA1CryptoServiceProvider();
            bool result = rsaPub.VerifyData(Data, sh, data);
            return result;
        }

        /// <summary>
        /// 加密
        /// </summary>
        /// <param name="resData">需要加密的字符串</param>
        /// <param name="publicKey">公钥</param>
        /// <param name="input_charset">编码格式</param>
        /// <returns>明文</returns>
        public static string encryptData(string resData, string publicKey, string input_charset) {
            byte[] DataToEncrypt = Encoding.GetEncoding(input_charset).GetBytes(resData);
            string result = encrypt(DataToEncrypt, publicKey, input_charset);
            return result;
        }


        /// <summary>
        /// 解密
        /// </summary>
        /// <param name="resData">加密字符串</param>
        /// <param name="privateKey">私钥</param>
        /// <param name="input_charset">编码格式</param>
        /// <returns>明文</returns>
        public static string decryptData(string resData, string privateKey, string input_charset) {
            byte[] DataToDecrypt = Convert.FromBase64String(resData);
            string result = "";
            for (int j = 0; j < DataToDecrypt.Length / 128; j++) {
                byte[] buf = new byte[128];
                for (int i = 0; i < 128; i++) {

                    buf[i] = DataToDecrypt[i + 128 * j];
                }
                result += decrypt(buf, privateKey, input_charset);
            }
            return result;
        }

        #region 内部方法

        private static string encrypt(byte[] data, string publicKey, string input_charset) {
            RSACryptoServiceProvider rsa = DecodePemPublicKey(publicKey);
            //MD5 sh = new MD5CryptoServiceProvider();//这里也可以使用MD5加密方式
            SHA1 sh = new SHA1CryptoServiceProvider();
            byte[] result = rsa.Encrypt(data, false);

            return Convert.ToBase64String(result);
        }

        private static string decrypt(byte[] data, string privateKey, string input_charset) {
            RSACryptoServiceProvider rsa = DecodePemPrivateKey(privateKey);
            //MD5 sh = new MD5CryptoServiceProvider();//这里也可以替换使用MD5方式
            SHA1 sh = new SHA1CryptoServiceProvider();
            byte[] source = rsa.Decrypt(data, false);
            char[] asciiChars = new char[Encoding.GetEncoding(input_charset).GetCharCount(source, 0, source.Length)];
            Encoding.GetEncoding(input_charset).GetChars(source, 0, source.Length, asciiChars, 0);
            string result = new string(asciiChars);
            //result = ASCIIEncoding.ASCII.GetString(source);
            return result;
        }

        private static RSACryptoServiceProvider DecodePemPublicKey(string pemstr) {
            byte[] pkcs8publickkey;
            pkcs8publickkey = Convert.FromBase64String(pemstr);
            if (pkcs8publickkey != null) {
                RSACryptoServiceProvider rsa = DecodeRSAPublicKey(pkcs8publickkey);
                return rsa;
            } else
                return null;
        }

        private static RSACryptoServiceProvider DecodePemPrivateKey(string pemstr) {
            byte[] pkcs8privatekey;
            pkcs8privatekey = Convert.FromBase64String(pemstr);
            if (pkcs8privatekey != null) {
                RSACryptoServiceProvider rsa = DecodePrivateKeyInfo(pkcs8privatekey);
                return rsa;
            } else
                return null;
        }

        private static RSACryptoServiceProvider DecodePrivateKeyInfo(byte[] pkcs8) {
            byte[] SeqOID = { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };
            byte[] seq = new byte[15];

            using (MemoryStream mem = new MemoryStream(pkcs8)) {
                int lenstream = (int)mem.Length;
                using (BinaryReader binr = new BinaryReader(mem)) {    //wrap Memory Stream with BinaryReader for easy reading

                    try {
                        ushort twobytes = binr.ReadUInt16();
                        if (twobytes == 0x8130)    //data read as little endian order (actual data order for Sequence is 30 81)
                            binr.ReadByte();    //advance 1 byte
                        else if (twobytes == 0x8230)
                            binr.ReadInt16();    //advance 2 bytes
                        else
                            return null;

                        byte bt = binr.ReadByte();
                        if (bt != 0x02)
                            return null;

                        twobytes = binr.ReadUInt16();

                        if (twobytes != 0x0001)
                            return null;

                        seq = binr.ReadBytes(15);        //read the Sequence OID
                        if (!CompareBytearrays(seq, SeqOID))    //make sure Sequence for OID is correct
                            return null;

                        bt = binr.ReadByte();
                        if (bt != 0x04)    //expect an Octet string
                            return null;

                        bt = binr.ReadByte();        //read next byte, or next 2 bytes is  0x81 or 0x82; otherwise bt is the byte count
                        if (bt == 0x81)
                            binr.ReadByte();
                        else
                            if (bt == 0x82)
                            binr.ReadUInt16();
                        //------ at this stage, the remaining sequence should be the RSA private key

                        byte[] rsaprivkey = binr.ReadBytes((int)(lenstream - mem.Position));
                        RSACryptoServiceProvider rsacsp = DecodeRSAPrivateKey(rsaprivkey);
                        return rsacsp;
                    } catch (Exception) {
                        return null;
                    } finally { binr.Close(); }
                }
            }

        }

        private static bool CompareBytearrays(byte[] a, byte[] b) {
            if (a.Length != b.Length)
                return false;
            int i = 0;
            foreach (byte c in a) {
                if (c != b[i])
                    return false;
                i++;
            }
            return true;
        }

        private static RSACryptoServiceProvider DecodeRSAPublicKey(byte[] publickey) {
            // encoded OID sequence for  PKCS #1 rsaEncryption szOID_RSA_RSA = "1.2.840.113549.1.1.1"
            byte[] SeqOID = { 0x30, 0x0D, 0x06, 0x09, 0x2A, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x01, 0x01, 0x01, 0x05, 0x00 };
            byte[] seq = new byte[15];
            // ---------  Set up stream to read the asn.1 encoded SubjectPublicKeyInfo blob  ------
            using (MemoryStream mem = new MemoryStream(publickey)) {
                using (BinaryReader binr = new BinaryReader(mem)) {   //wrap Memory Stream with BinaryReader for easy reading
                    try {

                        ushort twobytes = binr.ReadUInt16();
                        if (twobytes == 0x8130) //data read as little endian order (actual data order for Sequence is 30 81)
                            binr.ReadByte();    //advance 1 byte
                        else if (twobytes == 0x8230)
                            binr.ReadInt16();   //advance 2 bytes
                        else
                            return null;

                        seq = binr.ReadBytes(15);       //read the Sequence OID
                        if (!CompareBytearrays(seq, SeqOID))    //make sure Sequence for OID is correct
                            return null;

                        twobytes = binr.ReadUInt16();
                        if (twobytes == 0x8103) //data read as little endian order (actual data order for Bit String is 03 81)
                            binr.ReadByte();    //advance 1 byte
                        else if (twobytes == 0x8203)
                            binr.ReadInt16();   //advance 2 bytes
                        else
                            return null;

                        byte bt = binr.ReadByte();
                        if (bt != 0x00)     //expect null byte next
                            return null;

                        twobytes = binr.ReadUInt16();
                        if (twobytes == 0x8130) //data read as little endian order (actual data order for Sequence is 30 81)
                            binr.ReadByte();    //advance 1 byte
                        else if (twobytes == 0x8230)
                            binr.ReadInt16();   //advance 2 bytes
                        else
                            return null;

                        twobytes = binr.ReadUInt16();
                        byte lowbyte = 0x00;
                        byte highbyte = 0x00;

                        if (twobytes == 0x8102) //data read as little endian order (actual data order for Integer is 02 81)
                            lowbyte = binr.ReadByte();  // read next bytes which is bytes in modulus
                        else if (twobytes == 0x8202) {
                            highbyte = binr.ReadByte(); //advance 2 bytes
                            lowbyte = binr.ReadByte();
                        } else
                            return null;
                        byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };   //reverse byte order since asn.1 key uses big endian order
                        int modsize = BitConverter.ToInt32(modint, 0);

                        byte firstbyte = binr.ReadByte();
                        binr.BaseStream.Seek(-1, SeekOrigin.Current);

                        if (firstbyte == 0x00) {   //if first byte (highest order) of modulus is zero, don't include it
                            binr.ReadByte();    //skip this null byte
                            modsize -= 1;   //reduce modulus buffer size by 1
                        }

                        byte[] modulus = binr.ReadBytes(modsize);   //read the modulus bytes

                        if (binr.ReadByte() != 0x02)            //expect an Integer for the exponent data
                            return null;
                        int expbytes = (int)binr.ReadByte();        // should only need one byte for actual exponent data (for all useful values)
                        byte[] exponent = binr.ReadBytes(expbytes);

                        // ------- create RSACryptoServiceProvider instance and initialize with public key -----
                        RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
                        RSAParameters RSAKeyInfo = new RSAParameters {
                            Modulus = modulus,
                            Exponent = exponent
                        };
                        RSA.ImportParameters(RSAKeyInfo);
                        return RSA;
                    } catch (Exception) {
                        return null;
                    } finally { binr.Close(); }
                }
            }
        }

        private static RSACryptoServiceProvider DecodeRSAPrivateKey(byte[] privkey) {
            byte[] MODULUS, E, D, P, Q, DP, DQ, IQ;

            // ---------  Set up stream to decode the asn.1 encoded RSA private key  ------
            using (MemoryStream mem = new MemoryStream(privkey)) {
                using (BinaryReader binr = new BinaryReader(mem)) {    //wrap Memory Stream with BinaryReader for easy readin
                    try {
                        ushort twobytes = binr.ReadUInt16();
                        if (twobytes == 0x8130)    //data read as little endian order (actual data order for Sequence is 30 81)
                            binr.ReadByte();    //advance 1 byte
                        else if (twobytes == 0x8230)
                            binr.ReadInt16();    //advance 2 bytes
                        else
                            return null;

                        twobytes = binr.ReadUInt16();
                        if (twobytes != 0x0102)    //version number
                            return null;
                        byte bt = binr.ReadByte();
                        if (bt != 0x00)
                            return null;


                        //------  all private key components are Integer sequences ----
                        int elems = GetIntegerSize(binr);
                        MODULUS = binr.ReadBytes(elems);

                        elems = GetIntegerSize(binr);
                        E = binr.ReadBytes(elems);

                        elems = GetIntegerSize(binr);
                        D = binr.ReadBytes(elems);

                        elems = GetIntegerSize(binr);
                        P = binr.ReadBytes(elems);

                        elems = GetIntegerSize(binr);
                        Q = binr.ReadBytes(elems);

                        elems = GetIntegerSize(binr);
                        DP = binr.ReadBytes(elems);

                        elems = GetIntegerSize(binr);
                        DQ = binr.ReadBytes(elems);

                        elems = GetIntegerSize(binr);
                        IQ = binr.ReadBytes(elems);

                        // ------- create RSACryptoServiceProvider instance and initialize with public key -----
                        RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
                        RSAParameters RSAparams = new RSAParameters {
                            Modulus = MODULUS,
                            Exponent = E,
                            D = D,
                            P = P,
                            Q = Q,
                            DP = DP,
                            DQ = DQ,
                            InverseQ = IQ
                        };
                        RSA.ImportParameters(RSAparams);
                        return RSA;
                    } catch (Exception) {
                        return null;
                    } finally { binr.Close(); }
                }
            }
        }

        private static int GetIntegerSize(BinaryReader binr) {
            byte bt = 0;
            byte lowbyte = 0x00;
            byte highbyte = 0x00;
            int count = 0;
            bt = binr.ReadByte();
            if (bt != 0x02)        //expect integer
                return 0;
            bt = binr.ReadByte();

            if (bt == 0x81)
                count = binr.ReadByte();    // data size in next byte
            else
                if (bt == 0x82) {
                highbyte = binr.ReadByte();    // data size in next 2 bytes
                lowbyte = binr.ReadByte();
                byte[] modint = { lowbyte, highbyte, 0x00, 0x00 };
                count = BitConverter.ToInt32(modint, 0);
            } else {
                count = bt;        // we already have the data size
            }



            while (binr.ReadByte() == 0x00) {    //remove high order zeros in data
                count -= 1;
            }
            binr.BaseStream.Seek(-1, SeekOrigin.Current);        //last ReadByte wasn't a removed zero, so back up a byte
            return count;
        }

        #endregion

        #region 解析.net 生成的Pem
        private static RSAParameters ConvertFromPublicKey(string pemFileConent) {

            byte[] keyData = Convert.FromBase64String(pemFileConent);
            if (keyData.Length < 162) {
                throw new ArgumentException("pem file content is incorrect.");
            }
            byte[] pemModulus = new byte[128];
            byte[] pemPublicExponent = new byte[3];
            Array.Copy(keyData, 29, pemModulus, 0, 128);
            Array.Copy(keyData, 159, pemPublicExponent, 0, 3);
            RSAParameters para = new RSAParameters {
                Modulus = pemModulus,
                Exponent = pemPublicExponent
            };
            return para;
        }

        private static RSAParameters ConvertFromPrivateKey(string pemFileConent) {
            byte[] keyData = Convert.FromBase64String(pemFileConent);
            if (keyData.Length < 609) {
                throw new ArgumentException("pem file content is incorrect.");
            }

            int index = 11;
            byte[] pemModulus = new byte[128];
            Array.Copy(keyData, index, pemModulus, 0, 128);

            index += 128;
            index += 2;//141
            byte[] pemPublicExponent = new byte[3];
            Array.Copy(keyData, index, pemPublicExponent, 0, 3);

            index += 3;
            index += 4;//148
            byte[] pemPrivateExponent = new byte[128];
            Array.Copy(keyData, index, pemPrivateExponent, 0, 128);

            index += 128;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);//279
            byte[] pemPrime1 = new byte[64];
            Array.Copy(keyData, index, pemPrime1, 0, 64);

            index += 64;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);//346
            byte[] pemPrime2 = new byte[64];
            Array.Copy(keyData, index, pemPrime2, 0, 64);

            index += 64;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);//412/413
            byte[] pemExponent1 = new byte[64];
            Array.Copy(keyData, index, pemExponent1, 0, 64);

            index += 64;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);//479/480
            byte[] pemExponent2 = new byte[64];
            Array.Copy(keyData, index, pemExponent2, 0, 64);

            index += 64;
            index += ((int)keyData[index + 1] == 64 ? 2 : 3);//545/546
            byte[] pemCoefficient = new byte[64];
            Array.Copy(keyData, index, pemCoefficient, 0, 64);

            RSAParameters para = new RSAParameters {
                Modulus = pemModulus,
                Exponent = pemPublicExponent,
                D = pemPrivateExponent,
                P = pemPrime1,
                Q = pemPrime2,
                DP = pemExponent1,
                DQ = pemExponent2,
                InverseQ = pemCoefficient
            };
            return para;
        }
        #endregion

    }
}
